The present invention relates generally to the use of relays in aircraft electrical systems and more particularly to systems and methods for saving and indicating the status of a detected fault in the relays.
The primary functions of an aircraft electrical system are to generate, regulate and distribute electrical power throughout the aircraft. There are several different power sources on an aircraft that are used to supply power to aircraft electrical systems. These power sources can include engine driven AC generators, auxiliary power units, external power and ram air turbines. Aircraft electrical components operate on many different voltages levels using both AC and DC. However, most of the aircraft systems use 115V AC at 400 Hz or 28V DC. Further, 26V AC is also used in some aircraft for lighting purposes. DC power is generally provided by “self-exciting” generators containing electromagnets, where the power is generated by a commutator which regulates the output voltage of 28V DC. AC power, normally at a phase voltage of 115V, is generated by an alternator, generally in a three-phase system and at a frequency of 400 Hz.
Relays are commonly used in aircraft electrical systems to control the supply of power to various loads. A typical relay includes contacts that connect to a power supply and contacts that connect to a load. Electromechanical contacts are closed by a magnetic field generated by a coil. The coil is energized by a control current provided to the relay via a control input. Contact closure allows load current to flow.
Faults in aircraft electrical systems can be dangerous. In particular, faults in electrical loads such as fuel pumps can result in explosions. Examples of faults that can occur in an aircraft electrical system include ground faults (short circuit to ground) and arc faults (shorts between the power lines). Ground faults result in a net current imbalance, while arc faults do not.
Various fault interrupters are used for the aircraft electrical systems. These fault interrupters can include a universal fault interrupter (UFI), an arc fault circuit interrupter (AFCI), and thermally tripped circuit breakers (CBs) now commonly installed in cockpits.